1. Field of the Invention
The present invention relates to an elastic support for machines, in particular in connection with flexible supported base plates for machines with shafting arrangements.
2. Brief Description of the Background of the Invention Including Prior Art
The alignment is an important part in the setting up of large machines, for example of turbogenerator sets having relatively long running through shafting arrangements with several shaft bearings, in order to assure a disturbance free operation and a long life time. According to the present state of the art machines comprising several bearings and having a shafting with several rotors or aggregates are mounted as follows:
Upon separate delivery of rotors and casings, initially the bearings are aligned with respect to each other. After the insertion of the rotor upon rotation in one direction of rotation, the coupling imperfections such as eccentricity and impact and the play of the bearing are employed for realignment. At times also the elastic elements under the base plate are employed for the realignment of the shafting arrangement in the final mounting. However, a realignment of the shafting is not provided via forced deformations of the base plates with the aid of elastic set elements at the operation of the plant.
It is important for the economic operation of such plants that the required state of alignment at the start-up can be maintained as long as possible even after thermal expansion of the foundation. The stability of constant alignment is here decisive for example for the intervals between service and their economic significance justifies a considerable expenditure for the surveillance of the aligned state.
In view of this one has started to survey not only the quietness of running but also the shafting itself continuously and to consider also the causes of the changes of the alignment into the surveillance. The knowledge obtained in this fashion about the system behavior of shaft and foundation can have influence on future constructions of corresponding plants.
Relatively large bearing elasticities are provided upon use of flexible supported base plates at the elastic supporting of machines, which achieve that the vibrations generated in the machine are not radiated via the foundation into the environment.
The flexible supported base plate assumes a bending line on the elastic support elements corresponding to the bearing conditions in the situation. The bending line can be corrected by changing the support forces of the base plates, since the bending line depends on these support forces. The corresponding holds for the twisting and rotation of elastically supported plates and frames.
The elastic elements of the support can comprise rubber or neoprene or are formed by steel springs provided as so-called spring bodies. The transmission of vibrations is decreased based on the elastic support elements. At the same time multiple supported, statically indefinite supported foundations are transformed into a nearly statically determined symmetry. The lower restraining forces provided by the elastic support allow to produce foundations of less weight and more economically, as it would have been possible according to older codes requiring foundations resistant to bending such as the German Industrial Standard DIN 4024 of January 1955.
An elastic support is state of the art in particular at large or respectively long machines with several shaft bearings and continuous shafts such as employed for example in turbogenerator sets. At the present time the elastic elements are pretensioned before the construction of the foundation corresponding to the bending line of the foundation for the operating loads to be expected. During the mounting of the machine the foundation is also retensioned with the aid of shims or via hydraulic pistons or blocking spindels. However, up to now no retightening of the foundation has been provided to perform a resetting of the shafting arrangement during operation, in particular not as an automatic operation-connected alignment control.
At the elastic elements the bearing forces are proportional to relatively large deformation lengths. In contrast, in general the stiffness of a machine foundation can be considered to be substantially larger than the stiffness of the support elements.